Photomultiplier tube

ABSTRACT

A metal side tube ( 2 ), a glass faceplate ( 3 ), and a stem plate ( ) constitute a hermetically sealed vessel ( 5 ) for a photomultiplier tube. An edge portion ( 20 ) is provided at on open end (A) of the side tube ( 2 ). The edge portion ( 2 ) is embedded in the faceplate ( 3 ) in such a manner as to strike on the faceplate ( 3 ). Accordingly, high hermeticity at a joint between the side tube ( 2 ) and the faceplate ( 3 ) is ensured. The edge portion ( 20 ) extends upright in an axial direction of the side tube ( 2 ), so that the edge portion ( 20 ) can be embedded as close to a side face ( 3   c ) of the faceplate ( 3 ) as possible. This structure increases an effective sensitive area of the faceplate ( 3 ) to nearly 100%, and decreases dead area as close to 0 as possible. As described above, the photomultiplier tube ( 1 ) according to the present invention has enlarged effective sensitive area of the side tube ( 3 ) and enhanced hermeticity of the joint between the faceplate ( 3 ) and the side tube ( 2 ).

TECHNICAL FIELD

The present invention relates to a photomultiplier tube for detectingweak light incident on a faceplate by multiplying electrons emitted onthe faceplate.

BACKGROUND ART

Japanese patent Kokai publication No. Hei 5-290793 discloses aphotomultiplier tube includes an electron multiplier accommodated in ahermetically sealed vessel. The vessel has a metal side tube having aflange-shaped upper end. The flange-shaped end is welded to an uppersurface of a faceplate, thereby ensuring airtightness of the vessel.

Referring to FIG. 10, the conventional photomultiplier tube describedabove has a flange 101 bent inwardly at the whole upper end of the sidetube 100. The flange 101 results in the decrease in an effectivesensitive area of a faceplate 102. If the faceplate 102 has a size of 50mm×50 mm, and the flange 101 having a 1.5 mm width is fixed at andaround a periphery of the faceplate 102, the sensitive effective area isclearly considered 88%. This type of photomultiplier tube has succeededin obtaining more than 80% of a sensitive effective area. Recently, manyphotomultiplier tubes have been used and arranged as a unit for theirapplications. In those applications, photomultiplier tubes are requiredto have substantially 100% of sensitive effective area. In other words,photomultiplier tubes having substantially no dead sensitive area isnecessary. As long as the side tube 100 and the faceplate 102 are joinedby crimping the flange 101, a problem arises that the photomultipliertubes have more than 10% of dead sensitive area. If a lot ofconventional photomultiplier tube are juxtaposed densely, a substantialdead sensitive area may be easily produced. Japanese patent Kokaipublication No. Hei 5-290793 discloses that the side tube 100 and thefaceplate 102 are joined without using a flange. In the photomultipliertube disclosed, the faceplate 102 is just in contact with an edge of theside tube 100. This publication has no disclosure on how to join theside tube 100 and the faceplate 102. As described above, a leak mayoccur from the hermetically sealed vessel, when the faceplate 102 ismerely in contact with the edge of the side tube 100.

DISCLOSURE OF INVENTION

The present invention intends to solve the above problems. Especially, amain object of the present invention is to provide a photomultipliertube having enlarged effective sensitive area of a photocathode and ahermetically sealed vessel with enhanced hermeticity.

To attain the above objects, the present invention features aphotomultiplier tube including: a photocathode for emitting electrons inresponse to light incident on a faceplate; an electron multiplier in anhermetically sealed vessel for multiplying electrons emitted from thephotocathode; and an anode for generating an output signal based onelectrons multiplied by the electron multiplier. The hermetically sealedvessel includes: a stem plate for fixing the electron multiplier and theanode thereon by stem pins; a metal side tube having two open ends andenclosing the electron multiplier and the anode, the stem plate beingfixed at the open end; and the faceplate fixed to one open end of theside tube, the faceplate being made of glass. The side tube has an edgeportion at the other open end of side tube, the edge portion is embeddedin the side of the photocathode on the faceplate.

The photomultiplier tube according to the present invention has the edgeportion provided in the side tube. The edge portion is embedded in themanner that the edge portion penetrates into the glass faceplate. Thus,hermeticity at a joint between the side tube and the faceplate isensured. The edge portion of the side tube extends straight from theside tube rather than laterally from the side tube like a flange. In thecase when the edge portion is embedded as close to a side face of thefaceplate, i.e., an outline of the faceplate, as possible, the effectivesurface area of the faceplate 3 is increased to nearly 100%, and thedead area of the faceplate 3 is minimized at nearly 0. As describedabove, a photomultiplier tube according to the present inventionincreases an effective sensitive area of the faceplate and enhanceshermeticity between the side tube. and the faceplate on the basis of adifferent idea from those of conventional ones.

Preferably, the tip portion of the edge portion extends straight in thephotomultiplier tube according to the present invention. This structurefacilitates the penetration of an edge of the side tube into thefaceplate. Additionally, enlarged effective sensitive area of thefaceplate is ensured, because the edge portion is provided on a lineextending from the edge portion.

Preferably, the edge portion has a tip portion curved outwardly orinwardly with respect to the side tube in the photomultiplier tubeaccording to present invention. This structure can increase a contactarea of the edge portion embedded in the faceplate with the faceplate,thereby contributing to enhanced hermeticity of the joint between theside tube and the faceplate.

Preferably, the edge portion has a knife-edged tip in thephotomultiplier tube according to present invention. This structurefacilitates penetration of an edge of the side tube into the faceplate.Reliability and improved assembly of the photomultiplier tube areensured when the glass faceplate and the side tube are fused.

Preferably, the edge portion may have a single-edged tip. This structureincreases a contact area between the edge portion and the faceplate, andenhances conformability of the side tube with glass material.

The edge portion may have a double-edged tip. This structure facilitatespenetration of an edge of the side tube into the faceplate.

Preferably, the stem plate may be made of metal, an end face of the stemplate is in contact with an inner side wall of the side tube around theopen end thereof, and the inner side wall and the end face are weldedtogether. Accordingly, the photomultiplier tube has no projection like aflange at the lower end of the photomultiplier tube, because the sidetube and the stem plate are welded together while the inner side wall ofthe side tube is in contact with the end face of the stem plate. Thisstructure minimizes the whole size of the photomultiplier tube, thoughthe above structure is improper for resistance-welding. The abovestructure enables many photomultiplier tubes to be juxtaposed densely.Accordingly, the photomultiplier tube in which the metal side tube andthe metal faceplate are welded can be arranged at high density.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view showing one embodiment of a photomultipliertube according to the present invention;

FIG. 2 is a sectional view taken along the line II—II of FIG. 1;

FIG. 3 is an enlarged sectional view showing a joint of a side tube anda stem plate of the photomultiplier tube according to the presentinvention;

FIG. 4 is an enlarged sectional view showing a joint of a side tube anda faceplate of the photomultiplier tube according to the presentinvention;

FIG. 5 is an enlarged sectional view showing a first modification of aside tube in a photomultiplier tube according to the present invention;

FIG. 6 is an enlarged sectional view showing a second modification of aside tube in a photomultiplier tube according to the present invention;

FIG. 7 is an enlarged sectional view showing a third modification of aside tube in a photomultiplier tube according to the present invention;

FIG. 8 is an enlarged sectional view showing a forth modification of aside tube in a photomultiplier tube according to the present invention;

FIG. 9 is an enlarged sectional view showing a fifth modification of aside tube in a photomultiplier tube according to the present invention;and

FIG. 10 is an enlarged sectional view showing a conventional side tubeof a photomultiplier tube.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description will be made for explaining preferredembodiments of a photomultiplier tube according to the presentinvention, referring to the drawings.

FIGS. 1 and 2 illustrate a photomultiplier tube 1 including a side tube2 having substantially rectangular section and made of metal such asKovar metal and stainless steel. The photomultiplier tube 1 also has aglass faceplate 3 fused to one open end A of the side tube 2. Aphotocathode 3 a for converting light into an electron is formed on aninner side of the faceplate 3. The photocathode 3 a is formed byreacting alkali metal vapor with antimony deposited on the faceplate 3.The photomultiplier tube 1 has a stem plate 4 welded to the other openend B of the side tube 2. The stem plate 4 is made from metal such asKovar metal and stainless steel. The assembly of the side tube 2, thefaceplate 3, and the stem plate 4 forms a hermetically sealed vessel 5having a low height of substantially 10 mm.

A metal evacuating tube 6 is formed upright in the center of the stemplate 4. The metal evacuating tube 6 is used for evacuating the vessel 5with a vacuum pump (not shown) after assembly of the photomultipliertube 1 is finished. The metal evacuating tube 6 is also used tointroduce alkali metal vapor. into the vessel 5 during formation of thephotocathode 3 a.

The stem plate 4 has a plurality of metal stem pins 10 made from Kovarpass through the stem plate 4. The stem plate 4 has pin holes 4 a forthe stem pins 10 to pass therethrough. The pin hole 4 a is filled withtablet 11 made from Kovar glass as a hermetic seal. Each stem pin 10 issecured to the stem plate 4 by the tablet 11.

The vessel 5A accommodates an electron multiplier 7. The electronmultiplier 7 is supported in the vessel 5 by the stem pins 10. Theelectron multiplier 7 has a stacked structure of a block shape. Tenstages of flat dynodes 8 are stacked into an electron multiplier section9. Each dynode 8 is electrically connected to a tip of the stem pin 10.It should be noted that the stem pins 10 are classified into two groups:one group being connected to the dynodes 8; the other group beingconnected to an anode 12 described later.

The anodes 12 are positioned under the electron multiplying section 9 inthe electron multiplier 7, and secured to the top ends of the anodepins. A flat focusing electrode 13 is disposed between the photocathode3 a and the electron multiplying section 9 over the top stage of theelectron multiplier 7. A plurality of slit-shaped openings 13 a isformed in the focusing electrode plate 13. The openings 13 a arearranged parallel to each other in one direction. Slit-shaped electronmultiplying holes 8 a are formed in the dynode 8. The number of electronmultiplying holes 8 a is the same as that of the openings 13 a. Theelectron multiplying holes 8 a are arranged parallel to each other in ahorizontal direction.

Electron multiplying paths L are provided by arranging the electronmultiplying holes 8 a of each dynode 8 in a perpendicular direction tothe faceplate 3. A plurality of channels are formed in the electronmultiplier 7 by aligning the electron multiplying path L with thecorresponding opening 13 a of the focusing electrode plate 13. Theanodes 12 in the electron multiplier 7 are configured in an 8×8arrangement, so that each anode 12 is associated with a predeterminednumber of channels. Since the anode 12 is connected to the correspondingstem pin 10, output signals for each channel can be retrieved througheach anode pin 10B.

As described above, the electron multiplier 7 has a plurality of linearchannels. A predetermined voltage is applied across the electronmultiplying section 9 and the anodes 12 through the stem pin 10connected to a bleeder circuit (not shown). The photocathode 3 a and thefocusing electrode plate 13 are set to be at the same potential. Thepotential of the dynode 8 is increased from the top stage of dynodetoward the anodes 12. Therefore, incident light on the faceplate 3 isconverted to electrons at the photocathode 3 a. The electrons are guidedinto a certain channel by the electron lens effect generated by thefocusing electrode plate 13 and the first stage of dynode 8 on the topof the electron multiplier 7. The electrons guided into the channel aremultiplied by each stage of dynodes 8 while passing through the electronmultiplying paths L. The electrons strike the anodes 12 to generate anindividual output signal for the corresponding channel.

Referring to FIG. 3, when the metal stem plate 4 and the metal side tube2 are hermetically welded, an outer end face 4 b of the stem plate 4 isbrought into fit with an inner side wall 2 c at the open end B of theside tube 2. Next, the stem plate 4 is inserted through the open end Bto the side tube 2, so that the inner side wall 2 c at a lower end 2 aof the side tube 2 is brought into contact with an outer side face 4 bof the stem plate 4. Additionally, a lower end face 2 d of the side tube2 is approximately flush with a lower face 4 c of the stem plate 4, sothat the lower end face 2 d does not project lower than the stem plate4. Thus, the above structure extends the outer side wall 2 b at thelower end 2 a of the side tube 2 in the substantial axial direction ofthe tube 2, and eliminates lateral projection like a flange at the lowerend of the photomultiplier tube 1. In this state, a junction F betweenthe side tube 2 and the stem plate 4 is laser-welded by irradiating alaser beam on the junction F from a point directly below and external tothe junction F or in a direction toward the junction F.

By eliminating the flange-like overhang on the lower end of thephotomultiplier tube 1, it is possible to reduce the external dimensionsof the photomultiplier tube 1, though the above structure of thephotomultiplier tube 1 and the side tube 2 may be improper forresistance-welding. Further, when several photomultiplier tubes 1 arearranged, it is possible to minimize dead space between neighboringphotomultiplier tubes 1 as much as possible, thereby placing the sidetube 2 of neighboring photomultiplier tubes 1 close together. Laserwelding is employed to bond the stem plate 4 and side tube 2 as shown inFIG. 3 together in order to achieve a thin structure of thephotomultiplier tube 1 and to enable high-density arrangements of thephotomultiplier tube 1.

The above laser welding is one example for fusing the stem plate 4 andside tube 2. When the side tube 2 and the stem plate 4 are weldedtogether using the laser welding, it is unnecessary to apply pressureacross the junction F between the side, tube 2 and stem plate 4 incontrast to resistance welding. Hence, no residual stress is induced atthe junction F, thereby avoiding cracks from occurring at this junctionduring the usage. The usage of the laser welding greatly improves thedurability and sealability of the photomultiplier tube 1. Laser weldingand electron beam welding prevent generation of heat at the junction F,compared to the resistance welding. Hence, when the photomultiplier tube1 is assembled, there is very little effect of heat on the components inthe vessel 5.

The side tube 2 is formed by pressing a flat plate made from metal suchas Kovar and stainless steel into an approximately rectangularcylindrical shape having a thickness of approximately 0.25 mm and aheight of approximately 7 mm. The glass faceplate 3 is fixed to the openend A of the side tube 2 by fusion. As shown in FIG. 4, an edge portion20 is formed on an upper end of the side tube 2 which the glassfaceplate 3 faces. The edge portion 20 is to be brought into embedded inthe photocathode 3 a side of the faceplate 3 when a part of thefaceplate 3 is welded by a high-frequency heating. The edge portion 20is provided around the entire upper end of the side tube 2. The edgeportion 20 is curved inwardly and smoothly with an R-shaped portion 20 aon outer side wall 2 b of the side tube 2. A tip 20 b of the edgeportion 20 is formed like a knife-edge extending in the axial directionof the side tube 2. Hence the upper end of the side tube 2 can easilypierce the glass faceplate 3, thereby facilitating the assembly processand improving reliability when the side tube 2 and glass faceplate 3 arefused together.

When fixing the side tube 2 with the edge portion 20 having the aboveshape to the glass faceplate 3, the metal side tube 2 is placed on arotating platform (not shown) with the bottom surface of the glassfaceplate 3 contacting the tip 20 b of the edge portion 20 of the sidetube 2. Next, the metal side tube 2 is heated by a high-frequencyheating device while the glass faceplate 3 is pressed downwardly by apressure jig. At this time, the heated edge portion 20 gradually meltsthe glass faceplate 3, and penetrates therein. As a result, the edgeportion 20 is brought into embedded in the glass faceplate 3 whileforming an expanding portion 3 b at the lower end of the faceplate 3,ensuring a tight seal at the juncture between the glass faceplate 3 andside tube 2.

The expanding portion 3 b is formed on only a part of the faceplate 3 inthe vicinity of the edge portion 20. The formation of the expandingportion 3 b does not cause whole deformation over the side face 3 c ofthe faceplate 3. Accordingly, the formation of the expanding portion 3 bdoes not affect the edge shape of the faceplate 3 d. The flat shape ofthe faceplate 3 is maintained with reliability.

The edge portion 20 extends upward from the side tube 2 in an axialdirection of the side tube 2 rather than extends laterally from the sidetube 2 like a flange. The edge portion 20 can be embedded as close to aside surface 3 c of the faceplate 3 as possible. This structure canincrease the effective surface area of the faceplate 3 to nearly 100%and to minimize the dead area of the faceplate 3 at nearly 0.Additionally, the edge portion 20 is formed in the manner that it issmoothly curved inwardly of the side tube 2. Accordingly, a surface areaof the embedded edge portion 20 in the faceplate 3 is enlarged, whichcontributes to enhanced hermeticity of the vessel 5. The edge portion 20projects toward an interior of the side tube 2 by a small amount H of0.1 mm. The edge portion 20 may be formed by pressing.

It should be noted that a side tube for use with a photomultiplier tube1 according to the present invention is not limited to the embodimentsdescribed above. FIG. 5 shows a first modification. In thismodification, an edge portion 30 is to be embedded in the photocathode 3a side of the faceplate 3 by high frequency heating. The edge portion 30is formed at a tip portion (upper end) of the photocathode 3 a side ofthe side tube 2A. The edge portion 30 extends in an axial direction ofthe side tube 2, and is provided on the whole upper end of the side tube2A. The tip of the edge portion 20 is curved smoothly and outwardly ofthe side tube 2 with an R-shaped portion 30 a on an inner side 2 c. Thetip 30 b of the edge portion 30 is sharpened like a knife-edge extendingin the axial direction of the side tube 2. Accordingly, the upper end ofthe side tube 2A is easy to penetrate the faceplate 3. This structurefacilitates the assembly process and improves reliability when the sidetube 2 and glass faceplate 3 are fused together. In this embodiment, theedge portion 30 of the side tube 2A is brought into embedded in thefaceplate 3, while forming an expanding portion 3 b at the lower end ofthe faceplate 3. Therefore, hermeticity is ensured at a joint portion ofthe faceplate 3 and the side tube 2A. Additionally, the edge portion 30is curved smoothly and outwardly of the side tube 2, a surface area ofthe embedded edge portion 30 in the faceplate 3 is enlarged, so that acontact area between the side tube 2A and the faceplate 3 is alsoincreased. This structure contributes to enhanced hermeticity of thevessel 5. The edge portion 30 projects out of the side tube 2A by asmall amount H of 0.1 mm.

FIG. 6 shows a second modification. Referring to FIG. 6, an edge portion40 extends straight in an axial direction of the side tube 2B. In thisembodiment, the edge portion 40 is on an extending line of the side tube2B. The edge portion 40 has a simple shape in a manner that the sidetube 2B is just cut straight. A tip of the edge portion 40 may have around shape in order to improve conformability to glass and increase asurface area of the edge portion 40.

FIG. 7 shows a third modification. Referring to FIG. 7, an edge portion50 extends straight in an axial direction of the side tube 2C. The edgeportion 50 has a sharp tip consisting of double-edged faces 50 a, 50 a.This structure facilitates insertion of the side tube 2C into thefaceplate 3, when the side tube 2C is welded with the faceplate 3.

FIG. 8 show s a forth modification, in which an edge portion 60 extendsstraight in an axial direction of the side tube 2D. The edge portion 60has a single-edged tip end 60 a on an inner side face of the side tube2D. The knife-edge end 60 a has a substantially an arc-shaped outline inorder to enlarge a surface area of the edge portion 60 and enhanceconformability with glass material.

FIG. 9 shows a fifth modification, in which an edge portion 70 extendsstraight in an axial direction of the side tube 2E. The edge portion 70has a single-edged tip end 70 a on an outer side wall 2 b of the sidetube 2E. Thus, the tip of the edge portion 70 is sharp. The single-edgedface 70 a has an arc shaped outline in order to enlarge a surface areaof the edge portion 70 and enhance conformability with glass.

The edge portion 70 may have a spherical shape or an arrowhead section.

INDUSTRIAL APPLICABILITY

A photomultiplier tube according to the present invention may be usedwith an imaging device for a lower luminescent area such as a monitoringcamera, and night-vision equipment.

1. A photomultiplier tube comprising: a faceplate for receiving lightincident thereon; a photocathode for emitting electrons in response tothe light incident on the faceplate; an electron multiplier in ahermetically sealed vessel for multiplying electrons emitted from thephotocathode; and an anode for generating an output signal based onelectrons multiplied by the electron multiplier, wherein thehermetically sealed vessel includes: a stem plate having stem pins forfixing the electron multiplier and the anode thereon; a metal side tubehaving two open ends and enclosing the electron multiplier and theanode, the stem plate being fixed at one open end; and the faceplatehaving a surface for receiving the light thereon and an outer peripheryside therearound, the faceplate being fixed to the other open end ofthe- metal side tube, the faceplate being made from glass, and whereinthe metal side tube has an edge portion at the other open end of themetal side tube, the edge portion being embedded in the faceplate,thereby being positioned inside the outer periphery side of thefaceplate.
 2. The photomultiplier tube according to claim 1, wherein theedge portion has a tip end extending straight.
 3. The photomultipliertube according to claim 1, wherein the stem plate is made from metal,the metal side tube has an inner side wall extending between the twoopen ends, the stem plate has an outer peripheral face, the outerperipheral face of the stem plate is in contact with the inner side wallat the one open end of the side tube, to be welded therewith.
 4. Thephotomultiplier tube according to claim 1, wherein the edge portion hasa tip end curved toward one of an interior and an exterior of the metalside tube.
 5. The photomultiplier tube according to claim 1, wherein theedge portion has a tip end with a knife-edged face.
 6. Thephotomultiplier tube according to claim 5, wherein the tip of the edgeportion has a single-edged face.
 7. The photomultiplier tube accordingto claim 5, wherein the tip of the edge portion has a double edged face.8. A photomultiplier tube comprising: a faceplate; a photocathode foremitting electrons in response to light incident on the faceplate; anelectron multiplier in a hermetically sealed vessel for multiplyingelectrons emitted from the photocathode; and an anode for generating anoutput signal based on electrons multiplied by the electron multiplier,wherein the hermetically sealed vessel includes: a stem plate havingstem pins for fixing the electron multiplier and the anode thereon; ametal side tube having two open ends and enclosing the electronmultiplier and the anode, the stem plate being fixed at one open end;and the faceplate fixed to the other open end of the metal side tube,the faceplate being made from glass, and wherein the metal side tube hasan edge portion at the other end of metal side tube, the edge portionbeing embedded in a photocathode side on the faceplate, the edge portionhaving a tip end curved toward one of an interior and an exterior of themetal side tube.
 9. A photomultiplier tube comprising: a faceplate; aphotocathode for emitting electrons in response to light incident on thefaceplate; an electron multiplier in a hermetically sealed vessel formultiplying electrons emitted from the photocathode, and an anode forgenerating an output signal based on electrons multiplied by theelectron multiplier, wherein the hermetically sealed vessel includes: astem plate having stem pins for fixing the electron multiplier and theanode thereon: a metal side tube having two open ends and enclosing theelectron multiplier and the anode, the stem plate being fixed at oneopen end; and the faceplate fixed to the other open end of the metalside tube, the faceplate being made from glass, and wherein the metalside tube has an edge portion at the other open end of metal side tube,the edge portion being embedded in a photocathode side on the faceplate,the edge portion having a tip end with a knife-edged face.
 10. Thephotomultiplier tube according to claim 9, wherein the tip of the edgeportion has a single-edged face.
 11. The photomultiplier tube accordingto claim 9, wherein the tip of the edge portion has a double-edged face.